Pouch-type lithium secondary battery and fabrication method thereof

ABSTRACT

A pouch-type lithium secondary battery including a battery unit having a positive electrode plate, a negative electrode plate, and a separator between the positive and negative electrode plates; electrode tabs extending from each of the positive and negative electrode plates of the battery unit, respectively; a case having a space to accommodate the battery unit; a sealing surface along the periphery of the space; and a protection circuit board electrically connected to the electrode tabs, wherein portions of each of the electrode tabs extend outside the case, and are bent in an upright position with respect to a plane of the sealing surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/791,269 filed Mar. 3, 2004, now pending, and claims the benefit ofKorean Patent Application No. 2003-32554, filed on May 22, 2003 in theKorean Intellectual Property Office, the disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium secondary battery, and, moreparticularly, to an improved structure of connection between anelectrode tab and a protection circuit board electrically connectedthereto, and a pouch-type lithium secondary battery having the improvedconnection structure and a fabrication method thereof.

2. Description of the Related Art

With the development of portable electronic devices such as cellularphones, notebook-type computers, camcorders, and the like, increasedresearch into secondary batteries generally capable of charging anddischarging is being conducted. Lithium batteries are classified intonickel-cadmium (Ni—Cd) batteries, nickel-hydride (Ni-MH) batteries, andlithium secondary batteries. Specifically, the lithium secondarybatteries are being rapidly developed in view of their high operatingvoltage of 3.6 V or higher, which is approximately 3 times that of thenickel-cadmium (Ni—Cd) batteries or nickel-hydride (Ni-MH) batteries,and due to their excellent energy density per unit weight.

The lithium secondary batteries may be classified into liquidelectrolyte batteries and solid electrolyte batteries, according to theelectrolyte used. In general, batteries using a liquid electrolyte arereferred to as lithium-ion batteries, and batteries using a polymericelectrolyte are referred to as lithium polymer batteries.

The lithium secondary batteries may be manufactured in various shapes,and are typically formed in cylindrical and rectangular shapes. Lithiumpolymer batteries, which have attracted much attention recently, aremanufactured in a flexible pouch shape so that they are relatively freein view of shape design. Also, lithium polymer secondary batteries,which have excellent safety characteristics and are light in weight, areadvantageous in attaining miniaturized and lightweight portableelectronic apparatuses.

FIG. 1 shows a conventional pouch-type lithium secondary battery 10, andFIG. 2 is a partially extracted cross-sectional view of the lithiumsecondary battery shown in FIG. 1. Referring to the drawings, thelithium secondary battery 10 includes a battery unit 11, a case 12, anda space 12 a, provided in the case 12, in which the battery unit 11 isaccommodated.

The battery unit 11 includes a positive electrode plate 13, a negativeelectrode plate 14, and a separator 15 interposed therebetween. Thepositive electrode plate 13, the separator 15, and the negativeelectrode plate 14 are stacked in sequence. In such a state, the stackedstructure is laminated and wound in a jelly-roll type structure.

The positive electrode plate 13 and the negative electrode plate 14 areelectrically connected to a positive electrode tab 16 and a negativeelectrode tab 17, respectively. The positive and negative electrode tabs16 and 17 extend a predetermined length outward from a sealing surface12 b of the case 12. A portion where the positive electrode tab 16 andthe negative electrode tab 17 are electrically connected to the sealingsurface 12 b is wrapped by an insulating tape 18, thereby increasingsealing efficiency.

Unlike the cylindrical or rectangular lithium secondary battery, whichuse a thick metal plate as a packaging material, the case 12 ispreferably formed in a pouch type laminate constructed with a mediumlayer made of a thin metal foil, and inner and outer coatings fixed toboth surfaces of the medium layer, respectively, thereby providingbending flexibility.

The positive and negative electrode tabs 16 and 17, extending outsidethe sealing surface 12 b, are electrically connected to a protectioncircuit board 100. A safety element, such as a positive temperaturecoefficient (PTC) element, is provided in the protection circuit board100. The positive and negative electrode tabs 16 and 17 are respectivelyconnected to positive and negative electrode terminals 101 and 102provided in the protection circuit board 100. Thereafter, the protectioncircuit board 100 is mounted on the sealing surface 12 b of the case 12.

However, the conventional lithium secondary battery 10 has severalproblems. Unlike the cylindrical or rectangular lithium secondarybattery, the pouch-type lithium secondary battery 10 requires apredetermined width of the sealing surface 12 b of the case 12 to mountthe protection circuit board 100 thereon. In order to mount theprotection circuit board 100 on the sealing surface 12 b, the positiveand negative electrode tabs 16 and 17, extending outward from thesealing surface 12 b, are bent at least once.

In other words, as shown in FIG. 2, the positive and negative electrodetabs 16 and 17 are bent in an S-shaped form such that edges of thepositive and negative electrode tabs 16 and 17 are bent once at portionswhere they extend outward from the sealing surface 12 b, and are thenbent again in the opposite direction. The protection circuit board 100is seated on top of the thus-bent positive and negative electrode tabs16 and 17.

In order to mount the protection circuit board 100 in such a manner, itis necessary for the sealing surface 12 b to have a predetermined widthW1 corresponding to a width of the protection circuit board 100.

In recent years, the battery unit 11 of the lithium secondary battery 10has become larger in order to obtain a large capacity lithium secondarybattery. Thus, the space 12 a in which the battery unit 11 isaccommodated has tended to increase, while minimizing the area of thesealing surface 12 b. This has introduced a critical problem ofdeveloping efficient methods of attaching the protection circuit board100 to a limited area of the sealing surface 12 b.

Because the positive and negative electrode tabs 16 and 17 are bent inan S-shaped form, they may be easily cut at bent portions during abending process. Also, at portions where the positive and negativeelectrode tabs 16 and 17 extend outward from the sealing surface 12 b ofthe case 12, the positive and negative electrode tabs 16 and 17 may beelectrically connected to a medium layer exposed along the edge of thecase 12 by a cutting process, resulting in a short-circuit.

SUMMARY OF THE INVENTION

The present invention provides a pouch-type lithium secondary batteryhaving a minimized sealing surface of a case by providing an improvedconnection structure in which a protection circuit board electricallyconnected to electrode tabs is attached at an outer surface of a case,and a fabrication method of the lithium secondary battery.

The present invention also provides a pouch-type lithium secondarybattery which can prevent a short-circuit between a case and anelectrode tab by improving a bending structure of the electrode tabsextending outside the case, and a fabrication method of the lithiumsecondary battery.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

According to an aspect of the present invention, there is provided apouch-type lithium secondary battery comprising a battery unit having apositive electrode plate, a separator, and a negative electrode plate,wherein the separator is disposed between the positive and negativeelectrode plates, electrode tabs extending from each of the positive andnegative electrode plates of the battery unit, respectively, a casehaving a space to accommodate the battery unit, a sealing surface alongthe periphery of the space, and a protection circuit board electricallyconnected to the electrode tabs, wherein portions of each of theelectrode tabs extend outside the case, and are bent in an uprightposition with respect to a plane of the sealing surface.

According to another aspect of the invention, there is provided a methodof fabricating a lithium secondary battery, the method comprisingpreparing a battery unit comprising a positive electrode plate, anegative electrode plate, and a separator disposed between the positiveand negative electrode plates, disposing the battery unit in a spaceprovided in a case and sealing a sealing surface formed along theperiphery of the space, electrically connecting electrode terminals of aprotection circuit board to electrode tabs extending outside the case,wherein the electrode tabs are electrically connected to each of thepositive and negative electrode plates of the battery unit,respectively, and bending portions of each of the electrode tabsextending outside of the case through the sealing surface in an uprightposition with respect to a plane of the sealing surface of the case.

According to another aspect of the invention, there is provided apouch-type lithium secondary battery comprising a case providing a spaceto accommodate a battery unit, a sealing surface along the periphery ofthe space, and a protection circuit board electrically connected toelectrode tabs extending outside the case from the battery unit, whereinthe electrode tabs are bent in a thickness direction of the case, theelectrode tabs being respectively connected to electrode terminals ofthe protection circuit board.

According to another aspect of the invention, there is provided apouch-type lithium secondary battery comprising a battery unit,electrode tabs extending from the positive and negative electrode platesof the battery unit, a case having a space to accommodate the batteryunit and sealing surfaces formed along the periphery of the space,wherein the case is sealed at the sealing surfaces by thermal fusion,and a protection circuit board electrically connected to the electrodetabs. The battery unit includes: a positive electrode plate, aseparator, and a negative electrode plate, wherein the separator isdisposed between the positive and negative electrode plates. Theprotection circuit board is disposed in an approximately uprightposition with respect to planes of the sealing surfaces of the case.

The protection circuit board may be disposed on the sealing surface.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a plan view of a conventional lithium secondary battery;

FIG. 2 is a partly extracted perspective view of the lithium secondarybattery shown in FIG. 1;

FIG. 3 is a partly enlarged view of a lithium secondary batteryaccording to an embodiment of the present invention;

FIG. 4 is a cross-sectional view showing the lithium secondary batteryshown in FIG. 3;

FIG. 5 is a partly extracted perspective view of the lithium secondarybattery shown in FIG. 3; and

FIGS. 6A and 6B are partly extracted perspective views of the lithiumsecondary battery according to additional embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

As noted above, the lithium secondary batteries may be classified intoliquid electrolyte batteries and solid electrolyte batteries, accordingto the electrolyte used. In general, batteries using a liquidelectrolyte are referred to as lithium-ion batteries, and batteriesusing a polymeric electrolyte are referred to as lithium polymerbatteries.

FIG. 3 shows a pouch-type lithium secondary battery 30 according to anembodiment of the present invention.

Referring to FIG. 3, the lithium secondary battery 30 includes a batteryunit 31 and a case 32 accommodating the battery unit 31.

The battery unit 31 includes a positive electrode plate 33, a negativeelectrode plate 34 and a separator 35 interposed therebetween.

The positive electrode plate 33 has a positive electrode slurrycomprising a lithium-based oxide as a main component, a binder, aplasticizer, a conductive agent, and the like, coated on a positiveelectrode current collector formed of a strip-shaped metal foil, e.g.,an aluminum foil. A positive electrode tab 36 is welded to the positiveelectrode plate 33.

The negative electrode plate 34 has a negative electrode slurrycomprising a carbon material as a main component, a binder, aplasticizer, a conductive agent, and the like, coated on a negativeelectrode current collector formed of a strip-shaped metal foil, e.g., acopper foil. A negative electrode tab 37 is welded to the negativeelectrode plate 34.

At least one sheet of the separator 35 is disposed between the positiveelectrode plate 33 and the negative electrode plate 34 for insulationtherebetween. The separator 35 may be made of polyethylene,polypropylene, or a composite film of polyethylene and polypropylene. Inorder to prevent a short-circuit between the positive and negativeelectrode plates 33 and 34, it is advantageous, though not necessary,that the separator 35 is wider than the positive or negative electrodeplate 33, 34.

The case 32 includes an upper case body 32 a and a lower case body 32 bcoupled to the upper case body 32 a. The upper and lower case bodies 32a and 32 b are integrally coupled to each other along at least oneperiphery. When the upper and lower case bodies 32 a and 32 b are weldedto each other, the case 32 is shaped of a substantially rectangularsolid. A space 32 c in which the battery unit 31 is accommodated isprovided in at least one of the upper and lower case bodies 32 a and 32b.

After the battery unit 31 is accommodated in the space 32 c of the case32, the case 32 is sealed at upper and lower sealing surfaces 32 d and32 e by a method such as thermal fusion. The upper and lower sealingsurfaces 32 d and 32 e are provided at a portion where the upper andlower case bodies 32 a and 32 b are coupled to each other. The lowersealing surface 32 e is formed along the periphery of the space 32 c.The upper sealing surface 32 d is formed at a portion of the upper casebody 32 a corresponding to the lower sealing surface 32 e, the uppersealing surface 32 d being in contact with the lower sealing surface 32e, thus providing a sealing surface.

The upper and lower case bodies 32 a and 32 b are preferably, though notnecessarily, formed of substantially the same material, and areconstructed of multiple layers including an inner coating made of apolymeric insulating layer, a medium layer made of a metal foil formaintaining formability, and an outer coating made of a polymericinsulating layer.

The battery unit 31 having the above-described structure can be wound ina direction such that the positive electrode plate 33, the separator 35,and the negative electrode plate 34 are disposed sequentially in thatorder, that is, in a jelly-roll type structure. The wound battery unit31 is accommodated in the space 32 c. Here, edges of the positive andnegative electrode tabs 36 and 37, drawn out from the respectiveelectrode plates 33 and 34 of the battery unit 31, extend outside theclosed case 32.

An insulating tape 38 is wrapped around an outer surface of each of thepositive and negative electrode tabs 36 and 37. One end of theinsulating tape 38 is disposed between the upper and lower sealingsurfaces 32 d and 32 e, and is fusibly sealed together during thermalfusion of the case 32, while the other end of the insulating tape 38 isexposed to the outside of the case 32.

The ends of the positive and negative electrode tabs 36 and 37 exposedto the outside of the case 32 are electrically connected to a protectioncircuit board 300. The protection circuit board 300 prevents combustionor explosion of the battery 30 in the event of abnormal operation of thebattery, such as, for example, overcharging, by rapidly interruptingcurrent flow. As one example, a safety element such as a positivetemperature coefficient (PTC) element may be provided as the protectioncircuit board 300. The positive and negative electrode tabs 36 and 37,extending outward from the respective electrode plates 33 and 34 of thebattery unit 31, are electrically connected to the positive and negativeelectrode terminals 301 and 302, respectively, formed in the protectioncircuit board 300.

In the pouch-type lithium secondary battery 30 having theabove-described structure, as shown in FIG. 4, the upper sealing surface32 d and the lower sealing surface 32 e are thermally fused to eachother to seal the inside of the case 32 such that the battery unit 31 isprovided within the case 32.

Here, the ends of the positive and negative electrode tabs 36 and 37,extending outside the case 32, are electrically connected to thepositive and negative electrode terminals 301 and 302 of the protectioncircuit board 300, respectively, and the ends of the positive andnegative electrode tabs 36 and 37 are bent in a thickness direction ofthe case 32, which is described in more detail in FIG. 5.

Referring to FIG. 5, the wound battery unit 31, in which the positiveelectrode plate 33, the separator 35, and the negative electrode plate34 are laminated in that order, is disposed in the space 32 c formed bythe connection of the upper and lower case bodies 32 a and 32 b. Thepositive and negative electrode tabs 36 and 37, extending outward fromthe positive and negative electrode plates 33 and 34, respectively, passbetween the upper and lower sealing surfaces 32 d and 32 e, and extend apredetermined length outside the case 32. As described above, theinsulating tape 38 is wrapped around an outer surface of each of thepositive and negative electrode tabs 36 and 37 for the purpose ofelectrically isolating the positive and negative electrode tabs 36 and37 from the case 32.

The ends of the positive and negative electrode tabs 36 and 37 areconnected to the positive and negative electrode terminals 301 and 302of the protection circuit board 300, respectively. A portion of each ofthe positive and negative electrode tabs 36 and 37, extending outsidethe case 32, is bent from a leading edge of the upper and lower sealingsurfaces 32 d and 32 e in a thickness direction of the case 32, e.g., ina thickness direction of the lower case body 32 b. Here, the positiveand negative electrode tabs 36 and 37 may be bent at a substantiallyright angle.

In a state in which the positive and negative electrode tabs 36 and 37are bent, they are not further bent toward the upper and lower sealingsurfaces 32 d and 32 e, but are disposed parallel to an outer wall ofthe case 32 in an upright position. Accordingly, the positive andnegative electrode tabs 36 and 37 are perpendicular to a contact surfaceat which the upper and lower sealing surfaces 32 d and 32 e arecontacted.

In order to prevent a short-circuit between the positive and negativeelectrode tabs 36 and 37 and the case 32, the insulating tape 38 ispreferably, though not necessarily, wrapped around the outer surface ofthe positive and negative electrode tabs 36 and 37 at portions where thepositive and negative electrode tabs 36 and 37 are bent at the leadingedge of the upper and lower sealing surfaces 32 d and 32 e.

The protection circuit board 300, which is electrically connected to thepositive and negative electrode tabs 36 and 37, is disposed on the lowersealing surface 32 e. In other words, when the positive and negativeelectrode tabs 36 and 37 are bent perpendicular to the contact surfacebetween the upper and lower sealing surfaces 32 d and 32 e, theprotection circuit board 300 can be placed between the outer wall of thelower case body 32 b and the positive and negative electrode tabs 36 and37.

Also, since the protection circuit board 300 is disposed widthwise in anupright position between the outer wall of the lower case body 32 b andthe positive and negative electrode tabs 36 and 37, the upper and lowersealing surfaces 32 d and 32 e only have to have a minimum width W₂ foraccommodating the protection circuit board 300. Thus, the width W₂ ofthe upper and lower sealing surfaces 32 e and 32 d can be reducedcompared to the width W₁ of the conventional sealing surface (12 b shownin FIG. 2), in which a protection circuit board is not disposed in anupright position.

Alternatively, the portions of the positive and negative electrode tabs36 and 37 extending outside the case 32 may be bent at a right angletogether with the leading edge of the upper and lower sealing surfaces32 d and 32 e, so that the protection circuit board 300 may be placedbetween the outer wall of the lower case body 32 b and the bent positiveand negative electrode tabs 36 and 37.

Table 1 shows that the capacity of the battery unit 31 increases due toan increase in the area of the space 32 c as the protection circuitboard 300 is disposed in an upright position. TABLE 1 Sample 1 Sample 2Sample 3 Sample 4 Conventional 1165 mAh  984 mAh 857 mAh 843 mAhcapacity Capacity when 1220 mAh 1030 mAh 898 mAh 875 mAh sealing surfaceis reduced Increasing amount  55 mAh  46 mAh  41 mAh  32 mAh of capacityIncreasing ratio 4.7% 4.7% 4.8% 3.8% of capacity

Referring to Table 1, conventionally, samples 1-4 had capacities of 1165mAh, 984 mAh, 857 mAh, and 843 mAh, respectively, and a sealing surfacewidth of 4.5 mm. In the present invention, capacities of the samples 1-4were increased to 1220 mAh, 1030 mAh, 898 mAh, and 875 mAh,respectively, and a sealing surface width of 2.5 mm. That is, thesamples of the present invention showed capacity increases of 55 mAh, 46mAh, 41 mAh, and 32 mAh, respectively.

With reference to FIGS. 6A and 6B, other embodiments of the inventionare illustrated. As shown in these FIGS. the electrode terminals 301 and302 may be folded either once or twice in order to provide a position atwhich the protection circuit board 300 may be disposed. Of course, it isunderstood that these arrangements are only exemplary and that otherstructures are possible.

As described above, the pouch-type lithium secondary battery accordingto the present invention and a fabrication method thereof has severaladvantages, a few of which are described below.

First, since an electrode tab exposed outside a sealing surface of acase is bent from a leading edge of the sealing surface to be disposedin an upright position, and a protection circuit board electricallyconnected to the thus bent electrode tab is placed between an outer wallof the case and the electrode tab, an area of the sealing surface of thecase can be minimized.

Second, since the protection circuit board, which is electricallyconnected to the bent electrode tab, is disposed substantiallyperpendicular to the sealing surface, an area of the sealing surface ofthe case can be minimized.

Third, as the area of the sealing surface of the case is reduced, aninternal area of the case can be increased as much as the area of thesealing surface is reduced. Accordingly, the capacity of a battery unitaccommodated inside the case can be increased.

Fourth, since the electrode tab is disposed in an upright position withrespect to the case, damage due to bending of the electrode tab can beprevented, thereby ensuring safety of the battery.

Fifth, since an insulating tape is wrapped around a portion where theelectrode tab is bent from the leading edge of the sealing surface ofthe case, a short-circuit between the electrode tab and the case can beprevented.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A pouch-type lithium secondary battery comprising: a battery unitcomprising: a positive electrode plate, a separator, and a negativeelectrode plate, wherein the separator is disposed between the positiveand negative electrode plates; electrode tabs extending from thepositive and negative electrode plates of the battery unit; a casehaving a space to accommodate the battery unit and a sealing surfaceformed along the periphery of the space, wherein the case is sealed atthe sealing surface by thermal fusion; and a protection circuit boardelectrically connected to the electrode tabs, wherein the protectioncircuit board is disposed in an approximately upward position withrespect to planes of the sealing surfaces of the case.
 2. The pouch-typelithium secondary battery of claim 1, wherein the protection circuitboard is disposed on the sealing surface.
 3. The pouch-type lithiumsecondary battery of claim 1, wherein the protection circuit board isdisposed between an outer wall of the case and the electrode tabs. 4.The pouch-type lithium secondary battery of claim 1, wherein one end ofeach of the electrode tabs is bent in an upward position with respect tothe planes of the sealing surfaces.
 5. The pouch-type lithium secondarybattery of claim 4, wherein the electrode tabs and a leading edge of thesealing surface are bent a predetermined length in a thickness directionof the case.
 6. The pouch-type lithium secondary battery of claim 4,further comprising an insulating tape to provide electrical insulationbetween the electrode tabs and the sealing surface, wherein theinsulating tape is wrapped around the portions of the electrode tabsbent from a leading edge of the sealing surface.
 7. The batteryaccording to claim 1, wherein portions of the electrode tabs emergingfrom the case are folded into a U-shape and have the circuit boardpositioned on an outer surface of a curve thereof.
 8. The batteryaccording to claim 1, wherein portions of the electrode tabs emergingfrom the case are folded into an S-shape and have the circuit boardpositioned on an outer surface of a secondary curve thereof.
 9. Abattery including a battery unit having a positive electrode plate, aseparator, and a negative electrode plate wound together with theseparator being disposed between the positive and negative electrodeplates and electrode tabs extending from the electrode plates, thebattery comprising: a case, having a space with a thickness toaccommodate the battery unit, the case including upper and lowerportions to be sealed at sealing surfaces formed along the peripheriesof the upper and lower portions such that portions of the electrode tabsemerge therefrom; and a protection circuit board, having a long axis, tobe coupled to the electrode tabs and disposed with the long axis beingsubstantially parallel with a direction of the thickness of the case.10. The battery according to claim 9, wherein the portions of theelectrode tabs emerging from the case are folded into a U-shape and havethe circuit board positioned on an outer surface of a curve thereof. 11.The battery according to claim 9, wherein the portions of the electrodetabs emerging from the case are folded into an S-shape and have thecircuit board positioned on an outer surface of a secondary curvethereof.
 12. The battery according to claim 9, wherein the battery is apouch-type lithium secondary battery.
 13. The battery according to claim9, wherein the battery is a lithium polymer battery.
 14. The batteryaccording to claim 9, wherein the upper and lower portions are formed ofsubstantially similar material, and are constructed of multiple layersincluding an inner coating made of a polymeric insulating layer, amedium layer made of a metal foil to maintain formability, and an outercoating made of a polymeric insulating layer.
 15. A battery including abattery unit having a positive electrode plate, a separator, and anegative electrode plate wound together with the separator beingdisposed between the positive and negative electrode plates andelectrode tabs extending from the electrode plates, the batterycomprising: a case, having a space with a thickness to accommodate thebattery unit, the case including upper and lower portions to be sealedat planar sealing surfaces formed along the peripheries of the upper andlower portions such that portions of the electrode tabs emergetherefrom; and a protection circuit board, having a long axis, to becoupled to the electrode tabs and disposed with the long axis beingsubstantially perpendicular with the plane of the sealing surfaces. 16.The battery according to claim 15, wherein the portions of the electrodetabs emerging from the case are folded into a U-shape and have thecircuit board positioned on an outer surface of a curve thereof.
 17. Thebattery according to claim 15, wherein the portions of the electrodetabs emerging from the case are folded into an S-shape and have thecircuit board positioned on an outer surface of a secondary curvethereof.
 18. The battery according to claim 15, wherein the battery is apouch-type lithium secondary battery.
 19. The battery according to claim15, wherein the battery is a lithium polymer battery.
 20. The batteryaccording to claim 15, wherein the upper and lower portions are formedof substantially similar material, and are constructed of multiplelayers including an inner coating made of a polymeric insulating layer,a medium layer made of a metal foil to maintain formability, and anouter coating made of a polymeric insulating layer.